Refactor managemails to use signals

- use signals to trigger Celery tasks to create and delete mailboxes
- add generic TestCaseWithCeleryTasks class to handle celery task tests
  in a uniform way

gnuviechadmin/managemails/signals.py

@@ -0,0 +1,62 @@
+"""
+This module contains the signal handlers of the :py:mod:`managemails` app.
+
+The module starts Celery_ tasks.
+
+.. _Celery: https://www.celeryproject.org/
+
+"""
+import logging
+
+from django.db.models.signals import post_delete, post_save
+from django.dispatch import receiver
+
+from fileservertasks.tasks import create_file_mailbox, delete_file_mailbox
+from managemails.models import Mailbox
+from taskresults.models import TaskResult
+
+_LOGGER = logging.getLogger(__name__)
+
+
+@receiver(post_save, sender=Mailbox)
+def handle_mailbox_created(sender, instance, created, **kwargs):
+    """
+    Handles post creation actions on :py:class:`Mailbox <managemails.models.Mailbox>` instances.
+
+    :param sender: sender of the signal
+    :param instance: Mailbox instance
+    :param created: whether the instance has just been created
+
+    This signal handler starts a Celery_ task.
+
+    """
+    if created:
+        taskresult = TaskResult.objects.create_task_result(
+            "handle_mailbox_created",
+            create_file_mailbox.s(instance.osuser.username, instance.username),
+        )
+        _LOGGER.info(
+            "Mailbox creation has been requested in task %s", taskresult.task_id
+        )
+    _LOGGER.debug("mailbox %s has been %s", instance, created and "created" or "updated")
+
+
+@receiver(post_delete, sender=Mailbox)
+def handle_mailbox_deleted(sender, instance, **kwargs):
+    """
+    Handles cleanup actions to be done after deletion of a
+    :py:class:`Mailbox <managemails.models.Mailbox>` instance.
+
+    :param sender: sender of the signal
+    :param instance: Mailbox instance
+
+    This signal handler starts a Celery_ task.
+
+    """
+    taskresult = TaskResult.objects.create_task_result(
+        "handle_mailbox_deleted",
+        delete_file_mailbox.s(instance.osuser.username, instance.username)
+    )
+    _LOGGER.info(
+        "Mailbox deletion has been requested in task %s", taskresult.task_id
+    )